Docx Reader: Parse omml equations.
Docx Reader: Add new file, TexChar.

This will allow us to deal with unicode characters from word equations. This
part of the process will need to continue to be improved.
Docx Reader: Write LaTeX based on equations in word.

This is a first stab at writing out equations in LaTeX based on
omml equations in Word. There are some glitches: unicode chars not known to
LaTeX are silently skipped, and functions (such as `\oiiint`) not in the
standard LaTeX packages are inserted, which can lead to pdf compilation
errors (depending, of course, on your preamble).

Adding, for example, `\usepackage[charter]{mathdesign}` to the preamble will
allow you to use most of the more esoteric functions.
Merge pull request #1397 from jkr/equations

Docx Reader: Parse Docx OMML math/equations